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Mutations in MCOLN1 have been found to cause mucolipidosis type IV (MLIV; MIM 252650), a rare autosomal recessive lysosomal storage disorder found primarily in the Ashkenazi Jewish population. As a part of the successful cloning of MCOLN1, we constructed a 1.4-Mb physical map containing 14 BACs and 4 cosmids that encompasses the region surrounding MCOLN1 on human chromosome 19p13.3-p13.2-a region to which linkage or association has been reported for multiple diseases. Here we detail the precise physical mapping of 28 expressed sequence tags that represent unique UniGene clusters, of which 15 are known genes. We present a detailed transcript map of the MCOLN1 gene region that includes the genes KIAA0521, neuropathy target esterase (NTE), a novel zinc finger gene, and two novel transcripts in addition to MCOLN1. We also report the identification of eight new polymorphic markers between D19S406 and D19S912, which allowed us to pinpoint the location of MCOLN1 by haplotype analysis and which will facilitate future fine-mapping in this region. Additionally, we briefly describe the correlation between the observed haplotypes and the mutations found in MCOLN1. The complete 14-marker haplotypes of non-Jewish disease chromosomes, which are crucial for the genetic diagnosis of MLIV in the non-Jewish population, are presented here for the first time.

Anomalies in folate and homocysteine metabolism can result in homocysteinemia and are implicated in disorders ranging from vascular disease to neural tube defects. Two enzymes are known to methylate homocysteine, vitamin B(12)-dependent methionine synthase (MTR) and betaine-homocysteine methyltransferase (BHMT). BHMT uses betaine, an intermediate of choline oxidation, as a methyl donor and is expressed primarily in the liver and kidney. We report the discovery of a novel betaine-homocysteine methyltransferase gene in humans and mice. The human BHMT2 gene is predicted to encode a 363-amino-acid protein (40.3 kDa) that shows 73% amino acid identity to BHMT. The BHMT2 transcript in humans is most abundant in adult liver and kidney and is found at reduced levels in the brain, heart, and skeletal muscle. The mouse Bhmt2 gene shows 69% amino acid identity and 79% similarity to the mouse Bhmt gene and 82% amino acid identity and 87% similarity to the human BHMT2 gene. Bhmt2 is expressed in fetal heart, lung, liver, kidney and eye. The discovery of a third gene with putative homocysteine methyltransferase activity is important for understanding the biochemical balance in using methyltetrahydrofolate and betaine as methyl donors as well as the metabolic flux between folate and choline metabolism in health and disease.

Family and twin studies have indicated that genes influence susceptibility to panic and phobic anxiety disorders, but the location of the genes involved remains unknown. Animal models can simplify gene-mapping efforts by overcoming problems that complicate human pedigree studies including genetic heterogeneity and high phenocopy rates. Homology between rodent and human genomes can be exploited to map human genes underlying complex traits. We used regions identified by quantitative trait locus (QTL)-mapping of anxiety phenotypes in mice to guide a linkage analysis of a large multiplex pedigree (99 members, 75 genotyped) segregating panic disorder/agoraphobia. Two phenotypes were studied: panic disorder/agoraphobia and a phenotype (“D-type”) designed to capture early-onset susceptibility to anxiety disorders. A total of 99 markers across 11 chromosomal regions were typed. Parametric lod score analysis provided suggestive evidence of linkage (lod = 2.38) to a locus on chromosome 10q under a dominant model with reduced penetrance for the anxiety-proneness (D-type) phenotype. Nonparametric (NPL) analysis provided evidence of linkage for panic disorder/agoraphobia to a locus on chromosome 12q13 (NPL = 4.96, P = 0.006). Modest evidence of linkage by NPL analysis was also found for the D-type phenotype to a region of chromosome 1q (peak NPL = 2.05, P = 0.035). While these linkage results are merely suggestive, this study illustrates the potential advantages of using mouse gene-mapping results and exploring alternative phenotype definitions in linkage studies of anxiety disorder. © 2001 Wiley-Liss, Inc.